WO2016207169A1 - Method for locating a receiver in a positioning system - Google Patents

Abstract

The present invention relates to a method for locating at least one receiver (2) in a positioning system (1). The system includes: at least two generators (PL1, PL2), each generator emitting, on a single carrier, at least two signals that each have a different code, and a receiver (2) configured to detect the signals emitted by the generators (PL1, PL2). In said method: the receiver (2) measures, for each generator (PL1, PL2), the phase difference (δφ^j) between both signals emitted by the generator (PLj), and at least one geometric size, representing the position (x_r, y_r) of the receiver (2) in relation to the generators (PL1, PL2), is calculated on the basis of said measurements of the phase difference (δφ^j) in order to locate the receiver (2) in the positioning system (1).

Description

 Method of locating a receiver within a positioning system

The present invention relates to a method of locating at least one receiver within a positioning system and such a positioning system.

 The invention applies more particularly to systems using code multiplexing, also known as code division multiple access (CDMA), which is for example the case of GPS ("global positioning system" in English). and GNSS (Global Navigation Satellite System). These systems implement transmitters transmitting a signal comprising a carrier modulated by a code.

 For the vast majority of them, the known positioning systems rely on a triangulation or multilateration approach in order to define, in a global or local coordinate system, the coordinates of a mobile terminal, called a receiver.

 Other approaches rely on a set of measurements in polar coordinates in order to obtain the coordinates of the target terminal.

 These approaches are implemented at the terminal level, or at a more general level, such as a remote server with which the terminal communicates, or both on the terminal and on the server. The measurements lead to distances or angles.

 Known positioning systems are effective in outdoor, open air, so-called "outdoor" environment in English, but their performance is degraded in the interior, said "indoor" in English or when the sky is obstructed by buildings or high obstacles . In addition, the level of precision required indoors is higher than that required outdoors, the environment being smaller and denser in indoor information.

 It is also important to ensure the continuity of positioning between the outside and inside environments.

 Sensor networks offer excellent performance but their infrastructure is very constrained. The sensors used are ultrasonic, infrared, pressure sensors or electronic tags. The latter, in particular of the "Near Field Communication" (NFC) type, are more and more used, but do not allow a continuous positioning, neither in time nor in space.

 Techniques using mobile telecommunication networks, such as

GSM, UMTS, or fourth generation called "4G", or local, such as Bluetooth, Bluetooth Low Energy (BLE), Wi-Fi or Ultra Wide Band (ULB), require a infrastructure that can be deployed elsewhere, for purposes other than localization. However, it is also necessary to implement means specific to localization. An approach based on cell identification in the case of mobile networks, called "Cell-Id" in English, was developed for local tags, avoiding the use of the various calibration phases often required. This technique is not very precise.

 So-called "symbolic positioning" approaches have been developed, as described in the article by Magda Chelly and Nel Samama, "WIFI Indoor Symbolic Positioning System Implemented On a PDA", GNSS 2007, based on a hybrid solution using the identification of cell in mobile networks and GNSS signals, and offering a continuous, inaccurate and reliable positioning to date.

 Inertial systems are also used, implementing a small infrastructure but a complex mobile terminal and non-trivial modeling. These sensors are integrated in some smartphones today, "smartphones" in English.

 Sensor-based approaches divert these from their natural use to perform a location function.

 Systems using the analysis of local variations of the magnetic field allow good performance, but are not yet ready technically to be integrated in smartphones. Similar approaches rely on the use of magnetic beacons, and are similar to fingerprinting techniques commonly used by local telecommunications networks.

 Optical systems are also known, using smartphones integrated cameras, but leading to significant computational complexity for their processors. Image recognition systems are efficient but do not provide complete continuity: implementation constraints persist, these systems requiring a conscious action by the user to take the picture, and requiring a non-blurred image, which limits the movement of the mobile terminal during shooting.

The so-called "Li-Fi" technique, for "Light Fidelity" in English, is also emerging. This approach is similar to the "Cell-Id" technique mentioned above, but uses smartphones' light sensors, coding each luminaire according to its position via a modulation of light, the smartphone decoding this light. modulation to determine its position. The ergonomics of use of such an approach is not optimal.

 Radar-type systems rely on round-trip time measurements of a wave, to obtain a distance, and on arrival direction measurements in spherical coordinates. These systems represent a rather high simplification of the usual constraints of a positioning system, namely the synchronization between the parties involved and the spatial diversity required. A single transmitter is sufficient to determine a position. Nevertheless dedicated mobile terminals are needed. Some approaches use dual antennas spaced one wavelength from the signal, and measure the phase difference of the signals received from the two antennas to define the arrival angle of the transmitted signal.

 Solutions using GNSS signals have been developed, including A-GPS for "Assisted GPS" in English, and HSGNSS for "High Sensibility GNSS" in English, offering improved positioning performance in environments previously not covered by satellites, and can be implemented without dedicated infrastructure. These solutions are nevertheless limited in terms of detection, accuracy and time required to obtain a position.

 It is known from US Pat. No. 5,899,957 to correct phase-bearing GPS signals at an arbitrary position by using phase measurements received from different basic GPS stations whose position is known, to improve the positioning efficiency.

 U.S. Patent 4,646,096 discloses a method using the principle of movement of the satellite constellation around a receiver by measuring and storing carrier phase variations corresponding to the signals from said satellites, in order to determine the complete ambiguity of the measurements. corresponding signal code for single channel receivers.

 It is known, particularly from US Pat. No. 7,212,155, to use phase variation measurements of signal carriers from satellites, without using a base station, to progressively correct a hypothetical starting position of a receiver by movement.

US Pat. Nos. 7,671,794 and 6,449,165 disclose positioning systems using phase difference measurements made either on two separate antennas in reception or between two signals transmitted at different frequencies. The application WO 2014/060777 describes the positioning of a mobile terminal, using a signal sent by said terminal and received by multiple antennas of wireless multiple access points, and relying on phase difference calculations between the different antennas to obtain an angle of arrival of the signal on the antennas.

 Most of the previously described methods require the coupling or fusion of several techniques and / or technologies in order to achieve continuity of positioning between the exterior and interior environments.

 Known repelite approaches take advantage of the transmitted GNSS receivers and signals to enable a single GNSS receiver present in the mobile terminal to provide a location function.

 These approaches use the concept of pseudo-satellites, or "pseudolites", that is to say a network of terrestrial transmitters transmitting signals of the same structure as the signals sent by a satellite, as described in the article of Kee C. et al. Centimeter- Accuracy Indoor Navigation Using GPS-Like Pseudolites ", GPS World 2001, pages 14-20 The most accurate measurements of GNSS signals, which in particular allow centimeter positioning in good outdoor reception conditions, are used in these applications. approaches, offering high-quality experimental performance, and being reliable and easy to use, they will reduce the number of transmitters needed in the short term and simplify system management, such as eliminating synchronization or using low transmitters The signals developed in the framework of the European "Galileo" satellite positioning system project significantly reduce interference levels, suggesting that it will be possible to retain the bands used by GNSS signals to complete continuity of the localization function.

Geolocation using pseudolites calculates geometric intersections of spheres centered at known points, the positions of pseudolites, using the propagation time of the signals to measure the radius of the spheres, as described in chapter 2 of the Kaplan book E. and Hegarty C. "Understanding GPS Principles and Applications", Artech House, 2006, 2 ^nd edition. The propagation time of a signal can be measured by the code or the carrier of the signal. However, the phenomenon of multiple paths, called "multipath" in English, strongly affects measurement times outdoors, and even more indoors, because of the presence of many obstacles, such as described in Chapter 6 of the above-mentioned book and in the article by Fluerasu A. et al. It has been shown that it is difficult to obtain accurate measurements at more than 2 or 3 meters using only code measurements. in articles by Jardak N. and Samama N. "Short Multipath Insensitive Loop Discriminator Code", IEEE Transactions on Aerospace and Electronic Systems 2010, Vol 46, pp. 278-295, by Vervisch-Picois A. et al. "2D Indoor Dynamic Positioning Using GNSS Based Repeaters", ION GNSS 2006, and Jee GI et al. "Indoor Positioning Using Synchronized Time Switching GPS Repeater", ION GNSS 2005.

 The measurements of the carrier phase have the advantage of being less sensitive to the problem of multiple paths, and allow an accuracy of a few tens of centimeters, as presented in the articles by Rizos C. et al. "LocataNet: Intelligent Time-Synchronized Pseudolite Transceivers for CM-Level Stand-Alone Positioning", IAIN World Congress 2003, and I. Selmi et al. "Experimental Positioning Results of the Repainted Based Indoor Positioning System", IEEE International Conference on Indoor Positioning and Indoor Navigation 2012.

However, it is difficult to achieve absolute positioning before knowing the ambiguity of the phase of the carrier from each pseudolite. This ambiguity Nk corresponds to the result of the Euclidean division of the propagation distance by the wavelength of the carrier: D _PLh = <\> _k + .N _k , with DPLK the distance between the receiver and the pseudolite k, φ _Valeur the value of the phase of the carrier, and λ the wavelength, for example equal to 0.19 m for the GPS signal L1.

To solve this problem indoors, methods using principles related to the external environment are known, described in the articles of Kee C. et al. "Development of Indoor Navigation System Using Asynchronous Pseudolites", ION GPS 2000, by Xiaoguang Wan et al. "The Pseudolite-based Indoor Navigation System Using Ambiguity Resolution On The Fly", IEEE 3 ^rd International Symposium on Systems and Control in Aeronautic and Astronautics 2010, pages 212-217, and Puengnim A. et al. "Precise Positioning for Virtually Synchronized Pseudolite System", IEEE International Conference on Indoor Positioning and Indoor Navigation 2013, pages 1-8. Nevertheless, the assumption of linearity of the external environment is not valid indoors, the method described by Kee et al. is based on a non-linear version of the positioning algorithm described in chapter 2 of the book above, leading to a convergence of the unsecured algorithm in some situations. The methods described in the articles by Xiaoguang Wan et al. and Puengnim A. et al. based on the use of extended Kalman filters, the first implementing signal code measurements and the "Least square AMBiguity Adjustment" (LAMBDA) approach with a static initial position, and the second using the receiver movement for linearize the problem.

 The approaches described in the articles by Petrovski I. et al. "Precise Navigation Indoor", IEEE SICE Annual Conference 2004, vol 2, pages 1739-1744, and Kao Wei-Wen and Tsai Chin-Lang, "Carrier Phase Indoor Positioning using Pseudolites and INS" ION GNSS 2003, are based on the same principle but using the movement, from the base station in the first case, or the receiver, using an inertial sensor in the second case.

 Other approaches using only Doppler measurements are known, in particular described in the article by Schelkshorn S. and Detlefsen J. "Indoor Navigation Based on Doppler Measurements", IEEE Workshop on Positioning, Navigation and Communication 2007, pages 37-40. This article presents an approach simultaneously taking Doppler measurements of a moving object to locate by four sensors located at different positions. The article by Sakamoto Y. et al. "Doppler Positioning with a Movable Receiver Antenna and a Single Pseudolite for Indoor Localization", IEEE / ASME International Conference on Advanced Intelligent Mechatronics 2011, pages 19-24, presents a method of Doppler positioning only applied to a robot having a rotating antenna.

 There is a need to obtain a precise location within a positioning system, allowing continuity between the indoor and outdoor environments, and implementing a little complex infrastructure and compatible with all current mobile terminals.

 The aim of the invention is to meet this need and, according to one of its aspects, it achieves this through a method of locating at least one receiver within a positioning system, the system comprising:

 at least two generators, each generator emitting on the same carrier at least two signals each having a different code, and

a receiver configured to detect the signals emitted by the generators, process in which

 the receiver measures, for each of the generators, the phase difference between the two signals emitted by the generator, and

 according to these phase difference measurements, at least one geometric quantity representative of the position of the receiver relative to the generators is calculated in order to locate the receiver within the positioning system.

The two signals emitted by each generator are preferably emitted from two transmission zones of the generator distant from each other by a predefined distance di ₂ .

 The two signals emitted by each generator are advantageously emitted at the same frequency.

 The method according to the invention eliminates, during measurements, the knowledge of the absolute value of the distance separating the generator from the receiver. The invention produces unambiguous instantaneous measurements to obtain absolute positioning.

 The measurements of the geometric quantities representative of the position of the receiver relative to the generators are possible, with high precision, for example decimetric or centimeter, by phase difference measurements of radio signals, in particular of the GNSS type. The locating method according to the invention has a lower sensitivity to disturbances due to the propagation of the signals.

 The measurements are made for a single position of the receiver, which does not need to be mobile in the environment.

 Depending on the sign of the phase differences measured, the potential symmetries are eliminated and a single point is obtained.

 The invention requires only a reduced infrastructure, including a small number of generators, independent of each other, and not requiring synchronization with each other. The use of two-code generators makes it possible to use a receiver having only one antenna, corresponding to an "inverted radar".

 The invention allows continuity of positioning between the outer and inner environments.

 Once the initial position of the receiver is determined, positioning according to known methods can be achieved.

The invention can be implemented with all current mobile terminal receivers, including mobile phones. The method can be implemented indoors (indoor), serving for example for the positioning of objects in areas not covered by GPS or GNSS, for example buildings.

 The method according to the invention is advantageously based on the generation of GNSS type signals transmitted by radio, for example on RNSS frequencies, "Radio Navigation Satellite Services" in English, capable of being processed by GNSS receivers, at least as regards their digital processing.

 The frequency of the signals emitted by the generators can be arbitrary, but is preferably equal to 1.575 GHz, the signals being for example GNSS Galileo type.

 The term "issuer" may be substituted for the term "generator" and vice versa.

 Angle of arrival of the signals on the receiver

In a first embodiment of the invention, the geometric magnitude representative of the position of the receiver relative to a generator is the angle of arrival at signals emitted by the generator j on the receiver, as a function of the predefined distance di ₂ between the two generator emission zones and phase difference measurements δφ ⁷ , and defined by: α, = Arc cos

d ^J

 The angle is advantageously taken in the plane defined by the two emission zones of the generator and the receiver. It is considered that the angle in the middle of the two emission zones is identical to the angles coming directly from each zone towards the receiver, which is the case when the receiver is infinitely distant from said emission zones. It is advantageous that the distance between the transmission zones and the receiver is greater than at least ten times the predefined distance between the zones, being for example greater than 2 meters.

 At least one second angle calculation is advantageously performed with at least one second generator, in order to achieve a geometric intersection.

 The use of the angle as a geometrical magnitude makes the process simple, and operates even at a good distance, assuming that the signal lines are parallel.

 Distance between a generator and the receiver

In a variant or in combination, the geometric magnitude representative of the position (x _r , y _r ) of the receiver relative to a generator is the distance separating them, a function of the distances d ₁ , d ₂ between the position (x _a i, y _a i, x _a2 , y _a2 ) of each emission zone generator and the position of the receiver, defined for example by:

two-dimensional positioning (2D).

 After development, we can obtain:

4δφ ² ά ² = {d ₂ -d ² ^ j + δφ ⁴ -2δφ ² {ά ₂ -d ² ^ j, with:

d ₂ - d ² = (x a ₂ - x _r f + (y a ₂

^~ αΐ) r = ( ^X a2 ² - ^Χ 1 ² )

^~ αΐ) r

And, consequently, we can obtain the following expressions: d ² - d ² = 2AX _{ï 2} x _r + 2AY _l2 y "+ A ² X _2l + A ² Y _2l

[d ² - d ²⁾ = 4AX _l2 ² x _r ² + 4Δ7 ₁₂ + (Δ ² ₂₁ + A ² Y

+ 8AX ₁₂ AY ₁₂ x _r y _r + 4AX ₁₂ (A ² X ₂₁ + A ² Y _2l ) x _r + 4ΔΥ ₁₂ (Δ ² ₂₁ + Δ ² 7 ₂₁ ) 'in which:

= ^Xal ^{~ X}a2 ^{Qt AY}12 = y al ^" '«2 »

= ^X al ^{~ X} a2 ^{Qt YY} 12 = y al ^" '" 2 "

The following general relationship is obtained, as a function of the distances between the position of each transmission zone of the generator and the position of the receiver:

2δφ ² χ _α1 - AX _n (Δ ² ₂₁ + Δ ² 7 ₂₁ )]

-2δφ²γ_Α -Δ7₁₂(Δ¾ +Δ²7₂₁)]

-2δφ ² γ _Α -Δ7 ₁₂ (Δ¾ + Δ ² 7 ₂₁ )]

-2AX _l2 AY _l2 x _r y _{r +} δφ ² (χ _α1 ² _{+ γα1} ² ) ₊ ^δ ^ (Α ² Χ _{21 +} Δ ² 7 ₂₁ ) -1 (Δ ² _{21 +} A ² Y - *

whose overall form can be simplified as follows:

A (x _T - x _ref ) ² + β ( _Ύι - y _ref ) ² + C x _r y _r + D = 0, with A, BC and D on the one hand, and x _re f and y _re f d on the other hand, coefficients determined by the geometry of the problem and the phase difference measurement δφ. This amounts to determining a hyperbola for a two-dimensional positioning, or a three-dimensional (3D) hyperboloid on which the receiver is located, the emission zones of the generators being their homes.

At least one second generator is advantageously used to obtain a system of equations and an intersection of the hyperbolas, to obtain the position (x _r , y _r ) of the receiver.

 The use as a geometrical magnitude of the distance separating the receiver from a generator, and the expression in the form of hyperbolas, does not require any approximation.

 Generators

 Another object of the invention is, according to another of its aspects, a generator intended to be used within a positioning system, said system comprising at least one other generator and a receiver configured to detect the signals emitted by said generator and the other generator, said generator being configured to transmit on the same carrier at least two signals each having a different code, the receiver being configured to measure the phase difference between said two signals emitted by the generator.

 At least two generators are required for two-dimensional positioning and three generators for three-dimensional positioning to achieve geometric intersections and obtain a single point.

 The position of the generators within the positioning system is assumed to be known. The generators are preferably static.

 The two signals emitted by each generator can come from at least two antennas belonging to the generator and distant from each other by a predefined distance.

 The predefined distance from which the two antennas of the same generator are distant from each other is advantageously equal to the wavelength of the carrier of the signals emitted by the antennas. This provides unambiguous measurements at the receiver.

 The signals emitted by the same generator are preferably synchronized with each other, for example internally by the generator.

Each generator advantageously transmits on a different frequency. This eliminates the problem of the glare phenomenon or intrinsic interference between two signals emitting on the same frequency. Receiver

 Another object of the invention is, according to another of its aspects, a receiver intended to be used within a positioning system comprising at least two generators, each generator transmitting on the same carrier at least two signals each having a code different, the receiver detecting the signals emitted by the generators, the receiver being configured to:

 measure, for each of the generators, the phase difference between the two signals emitted by the generator, and

 based on these phase difference measurements, at least one geometric magnitude representative of the position of the receiver relative to the generators is calculated in order to locate the receiver within the positioning system.

 The receiver advantageously comprises a phase-locked loop configured to measure the phases of the signals emitted by the generators.

 The receiver is advantageously multichannel, at least one first channel being configured to detect the first signal of a generator, and at least one second channel being configured to detect the second signal of the same generator.

 The receiver can be static or mobile.

 As a receiver can be used a standard receiver, GNSS for example, no modification of such a receiver being necessary to implement the method according to the invention.

 Positioning system

 Another aspect of the invention is a positioning system comprising:

 at least two generators, each generator emitting on the same carrier at least two signals each having a different code, and

 a receiver detecting the signals emitted by the generators, the system being configured so that:

 the receiver measures, for each of the generators, the phase difference between the two signals emitted by the generator, and

according to these phase difference measurements, at least one geometric magnitude representative of the position of the receiver relative to the generators is calculated in order to locate the receiver within the positioning system. Variations in receiver-transmitter distance

 As a variant or in combination, the subject of the invention is also a method of locating at least one receiver within a positioning system, the system comprising:

 at least two transmitters, each transmitter emitting a signal comprising a carrier modulated by a code, and

 a mobile receiver within the system, configured to detect the signals emitted by the transmitters,

process in which

 during the movement of the receiver, from a predefined initial position of the latter, successive measurements of the carrier phase of the signal emitted by each transmitter are made for different subsequent positions of the receiver,

 the variations of the phase of the carrier of the signals are calculated between each subsequent position of the receiver for which the phase has been measured and the estimated initial position of the receiver, for each transmitter, and

 these phase variations are used to calculate the variation in distance between the receiver and the transmitters, in order to determine the actual initial position of the receiver within the positioning system.

 The combination of the two processes defined above is of some interest. A complete positioning system implementing these two methods makes it possible, from the same phase measurements, to have at least three operating modes: an absolute positioning by making differences, at a given instant, between the two antennas of a generator and that for several generators, then a relative positioning from the position obtained, a decimetric precision, by phase difference measurements at successive instants, then an absolute positioning in motion by analysis of the evolution of the phase of the carriers from the various antennas at several successive times.

As mentioned previously, and as represented in FIG. 6, a pseudolite PL1, PL2, PL3, PL4 is a transmitter synchronized on a global system 31 of reference time, common to the entire constellation. It is possible to measure the pseudo-distance PRk (t) of a pseudolite plk at a time t, or "pseudorange" in English, corresponding to an indirect measurement of distance by locating the instant of reception of a signal coming from pseudolite and dated at issue, when the clocks pseudolite and receiver 30 are not synchronized. This measure can be expressed by:

V (x (t) - x _plk ) ² + (y (t) - y _plk ) ² + (z (t) - z _plk ) ² + cb (t) = PR _k (t), with (x (t ), y (t), z (t)) the coordinates of the receiver at time t, (x _p ik, y _P ik, z _p ik) the pseudolite coordinates plk, assumed to be known, c the speed of light and b (t) the clock bias between the constellation reference time and the receiver clock at time t. It should be noted that the height z is considered to be known in the case of two-dimensional positioning.

 The pseudo-distance can be measured using the code delay or the phase of the carrier of the incoming signal. In the case where the phase is used, the expression becomes:

^] (x (t) - x _plk ) ² + (y (t) - y _plk ) ² + (z (t) - z _plk ) ² + cb (t) = <j) _k (t) + .N _k , with (f> _k the phase of the carrier depending on the time t, λ the wavelength and Nk the ambiguity of the phase introduced previously, not dependent on time.

Since the ambiguity of the phase does not depend on time, it is advantageous to eliminate it by measuring the pseudo-distance of an emitter according to the invention at two successive moments t ₁ and t ₂ and to subtract the equations obtained. :] (x (t ₂ ) - x _plk ) ² + (y (t ₂ ) - y _plk ) ² + (z (t ₂ ) - z _plk ) ²

-yj (x (ti) ^~ x _{≠ k} ) ² + (J> (* i) ^" y _≠ k) ² + (z (* i) ^" _≠ k)

For the sake of simplicity, in the following, a two-dimensional positioning will be considered, and the unknowns x (ti), y (ti), x (t ₂ ), y (t ₂ ) and b (t ₂ ) -b (ti) will be noted respectively xi, yi, x ₂ , y _{2 and} Abi ₂ , and the phase ()> k (tj) will be denoted by φ ^.

At least a third time t ₃ can be considered, corresponding to a position of the receiver x ₃ , y ₃ and a clock bias b (t ₃ ), to obtain a new measurement and increase the number of equations. The number of transmitters n _p i is advantageously a function of the dimension m of the positioning and the number of measurements k _pt made for different positions of the receiver:

This relationship makes it possible to know the minimum number of emitters necessary for the proper implementation of the method according to the invention.

 The dimension m of the positioning may be equal to two or three, respectively corresponding to a positioning in two or three dimensions.

 In the case of a limited number of transmitters, in particular two transmitters, additional indications may facilitate the determination of the initial position of the receiver, for example an observation of the area of the environment in which the receiver operates and of its trajectory. , making it possible to discriminate certain symmetries, and / or to determine whether or not the path of the receiver intersects the straight line passing through the two transmitters.

 The method according to the invention makes it possible to adapt to the required and available conditions: a greater number of emitters can be used if few measurements of the phase have to be made, for example to obtain quickly the position of the receiver, or, on the contrary, a smaller number of transmitters can be used if a reduced infrastructure is desired, a higher number of measurements of the phase then being realized. The length of the displacement of the receiver between two positions is also to be determined, according to the geometry of the region covered by the positioning system.

 The system of equations obtained according to the number of measurements made can be linearized and iteratively solved by Newton's algorithm or by the least squares algorithm, called "Least-Square" in English.

The variation of the phase of the carrier can be calculated between a subsequent position (xj, y, Zj) and the predefined estimated initial position (xi, yi, zi) of the receiver, corresponding to the instant ti and the subsequent instant tj, by the relation: (y ^{~ x} pik) ^{2 +} (yj -y _P ik) ² + ( ^z - ^z _P ik) ^{2 ~} Λ] ( ^χ Ι - ^x _P ik y + (ji - y _P ik y + ( ^z - ^z _P ik y

Cab + _Xi

 = Ι - Ι

A first-order Taylor series can be used to calculate the variation of the carrier phase:

-ax _k dxi - a _yk ^d Vi + a ^J _Xk d _Xj + a ^ dy, - + c. dAb ^ - = - - (p _k - p¾,

I 2 2 2

with Pk = ^ (x _u - * _P ik) + (y _u - Yik) + (z - z _p ik) + c. b (t _u ), (Xplk-Xu) u

ax _k - and a yk

(xu-xpik) + (y _u -y _P ik) + (zz _P ik) (y _P ik-y _u )

(xu-xpik) ² + (yu-y _P ik) ² + (zz _P ik) "

The values dxi, dyi, dxj, dyj and dAbij, corresponding to the variation in distance between the estimated initial position and the actual initial position of the receiver, are advantageously determined at each iteration of the algorithm.

 A matrix product is advantageously used to calculate the distance variation ΔΧ between the receiver and the emitters: H. ΔΧ = άΔφ,

_ρ1) ρ₁) ) p_lJ.

_ρ1 ) ρ ₁ )) p _l J.

The matrix H can be inverted to obtain the matrix of variations of distance ΔΧ = dAcJ H ^-1 .

 The method according to the invention is preferably reiterated as long as the distance variation between the receiver and the transmitters is greater than a first predefined threshold.

 The choice of the estimated initial position of the receiver is fundamental for the convergence of the algorithm. The method according to the invention advantageously comprises a step in which, if the variation in distance between the receiver and the emitters is greater than a second predefined threshold, the predefined estimated initial position of the receiver is modified. The phase measurements can be reiterated from this new estimated initial position.

 When the distance variation between the receiver and the emitters is less than the first predefined threshold, it is checked whether the initial position of the receiver thus determined belongs to the region covered by the positioning system, delimited by the positions of the emitters.

 If the initial position of the determined receiver belongs to the region covered by the positioning system, the estimated initial position of the receiver is advantageously retained as the actual position, otherwise the method according to the invention can be repeated.

 The emitters can be such as the generators defined above.

The invention will be better understood on reading the following description, non-limiting examples of implementation thereof, and on examining the appended drawing, in which: FIG. 1 schematically represents a positioning system in which a method according to the invention can be implemented,

 FIG. 2 represents the geometry implemented in a positioning system according to the invention,

 FIGS. 3 to 5 are curves showing the performances of the method according to the invention,

 FIG. 6 schematically represents a positioning system, according to the prior art, using pseudolites,

 FIG. 7 illustrates stages of implementation of a variant of the method according to the invention,

 FIG. 8 diagrammatically represents a positioning system in which a variant of the method according to the invention can be implemented, and

 FIG. 9 illustrates a trajectory result of a receiver obtained by the implementation of a variant of the method according to the invention.

 FIG. 1 shows an exemplary positioning system 1 in which the invention can be implemented.

 The system comprises a receiver 2 and three generators PL1, PL2, PL3 forming a local constellation. The system 1 can be implemented indoors (indoor), for example inside a building, or outside in a very urban area, between very high walls for example.

Each generator PL1, PL2, PL3 emits, in the example described, on the same carrier, two signals each having a different code. These two signals are emitted from two transmission areas PL1 i, PL1 ₂ of the generator PLI distant from each other by a predefined distance di ₂ . In the example described and preferably, the two signals emitted by each generator PL1, PL2, PL3 come from two antennas belonging to the generator and distant from each other by a predefined distance equal to the wavelength of the carrier of the signals emitted by the antennas.

The signals emitted by the same generator are preferably synchronized with each other. Each generator PL1, PL2, PL3 emits preferably on a different frequency. The signals emitted by the generators PL1, PL2, PL3 are for example GNSS signals of frequency equal to 1.575 GHz. The receiver 2 is configured to detect the signals emitted by the generators. The latter are for example received by the antenna of the receiver 2 and then amplified and converted to IF intermediate frequency lower than their initial frequency.

These signals are in the example considered sampled, then digitized before being processed by the reception channels of the receiver 2, being multichannel. These reception channels may implement tracking loops. The receiver 2 advantageously comprises a phase-locked loop configured to measure the phase φ _Ιζ of the carrier of the signals emitted by the generators.

The receiver 2 is advantageously configured to measure, for each of the generators PLI, PL2, PL3, the phase difference δφ ⁷ between the two signals emitted by the generator PLj.

As defined above, as a function of these phase difference measurements δφ ⁷ , the receiver 2 is advantageously configured to calculate at least one geometric quantity representative of the position of the receiver relative to the generators PL1, PL2, PL3, in order to obtain its position (x _r , y _r ) within the system 1.

entre les deux zones d'émission du générateur et des mesures de différence de phase δφ^] : a . = Arc cos In the example of FIG. 2, and as defined above, the geometric magnitude representative of the position (x _r , y _r ) of the receiver 2 with respect to a generator PLj is the angle of arrival oy of the signals emitted by the PLj generator on the receiver, according to the predefined distance

between the two generator emission zones and phase difference measurements δφ ^] : a. = Arc cos

at ^J

In a variant, the geometric magnitude representative of the position (x _r , y _r ) of the receiver 2 with respect to a generator PLj is the distance separating them, a function of the distances (di, d ₂ ) between the position (x _a i, _is i, x _a2, y _a2) of each PLji emission area, PLj ₂ nérateur PLj and the position (x _r, y _r) of the receiver 2:

 FIGS. 3 to 5 represent results obtained by implementing the invention in a hall of 20 m by 20 m, in which two generators PL1 and PL2 are positioned at the positions (0, 0) and (20, 0), being thus positioned on the same side of the hall.

The method according to the invention is implemented, as defined above, to find a receiver 2, located at the coordinates (5; 15) of the hall. About 660 Phase difference measurements are made to evaluate the performance of the method according to the invention.

 Figure 3 shows the distribution of position errors by measurement, corresponding to the distance between the position of the calculated receiver 2 and its actual position. According to Figure 3, the positioning accuracy seems to be centered on about thirty centimeters.

 Figure 4 shows the distribution of position errors as a function of the measurement errors of the phase of the signals.

 FIG. 5 shows the positions of the receiver 2 calculated according to the invention in the Oxy plane, the desired point being represented by a square at the coordinates (5, 15) and the various calculated points being represented by dark diamonds. Sliding averages on 10 points were made, represented by triangles, to confirm that the accuracy of positioning is of the order of thirty centimeters. The light diamond represents the overall average of the dot obtained on the 650 measurements, which is 7.5 cm from the actual position of the receiver 2.

 FIG. 8 shows an example of a system 1 in which a variant of the method according to the invention can be implemented, of which steps are illustrated in FIG. 7.

 The system 1 comprises a mobile receiver 2 within the system 1 and a plurality of transmitters PL1, PL2, PL3, PL4 forming a local constellation. As shown in Figure 6, the system 1 can be implemented indoors (indoor), for example inside a building, or outside in a very urban area, between very high walls by example.

 Each transmitter PL1, PL2, PL3, PL4 preferably transmits a signal comprising a carrier modulated by a code. The emitters may be the generators described above. In this case, only one antenna per generator is advantageously considered.

As explained previously, and as represented in FIG. 7, during a step 11, a predefined estimated initial position X is chosen for the receiver 2. During its displacement within the positioning system 1, from this estimated initial position during a step 12, the receiver 2 makes successive measurements of the phase φ _Ιζ of the carrier of the signal transmitted by each transmitter PLI, PL2, PL3, PL4, for different subsequent positions of the receiver (xj, y, Zj).

During a step 13, the variations Δφ of the phase of the carrier of the signals are calculated between each subsequent position of the receiver 2 for which the phase φ _Ιζ has been measured and the estimated initial position of the receiver, for each transmitter PLI, PL2 , PL3, PL4. The matrix άΔφ defined above is created during a step 13bis.

 In order to calculate the distance variation ΔΧ between the receiver 2 and the transmitters and to determine the actual initial position of the receiver 2 within the positioning system 1, the matrix H defined above is created during a step 14 and is inverted during of a step 15. The variation of distance ΔΧ is calculated during a step 16.

 The variation of distance ΔΧ thus calculated and the predefined estimated initial position X of the receiver 2 are added during a step 17 to form a new initial position X.

During a step 18, the distance variation ΔΧ is compared with a second predefined threshold ε ₂ . If ΔΧ is greater than this second predefined threshold, the predefined estimated initial position x of the receiver 2 is modified, the phase and phase Δφ phase measurements being reiterated from this new estimated initial position.

If ΔΧ is less than this second predefined threshold ε ₂ , it is compared with a first predefined threshold ει, the method according to the invention being advantageously reiterated, starting from step 14, as long as the distance variation ΔΧ between the receiver and the transmitters is greater than this first predefined threshold.

 When the distance variation ΔΧ between the receiver 2 and the emitters is less than the first predefined threshold ει, it is verified, in a step 19, whether the initial position of the receiver thus determined belongs to the region covered by the positioning system 1 , delimited by the positions of the transmitters.

 If the initial position of the determined receiver belongs to the region covered by the positioning system 1, the estimated initial position X of the receiver 2 is retained as the actual position in a step 20, otherwise, the process is repeated.

The first predefined threshold is between 10 ^"5 m and 10 ^{" 1} m, being for example equal to 10 ^{~ 2} m. The second predefined threshold is between 10 ² m and 10 ⁵ m, being for example equal to 10 ³ m. Figure 9 shows results obtained by implementing the invention in a U-shaped urban canyon of 20 m by 30 m, formed by tall buildings. In this example, four transmitters are deployed on the top floor of buildings, at an altitude of approximately 18 m.

 A receiver 2 is moving in this environment. The receiver 2 has the estimated initial position PO, then makes a round trip between the positions PO and P3 through the subsequent positions PI and P2, then goes from the position PO to the position P4. The locating method of the receiver 2 according to the invention is implemented and the positions obtained are compared with the real trajectory, as can be seen in FIG. 9. The reconstituted trajectory obtained is very close to the real trajectory, known beforehand for the Experiment requirements, the gap remaining below 50 cm, as shown in the table below showing the error and average error for each position.

Positions P3 and P4 give the largest errors because they are more difficult to estimate by the path configuration, corresponding to a multiple path and cycle slips accumulating sources of error. The method according to the invention has thus been used to correct the position P4, by using a further measurement at an intermediate position between P3 and P4, leading to the result P4c in the table above, giving a lower error.

The last column of the table shows the results obtained for extended horizontal dilution of precision, or "extended horizontal dilution of precision" in English, a value specifying the influence of the geometry of the environment on the accuracy of the positioning system, and adapted to the method according to the invention, thus representing the influence of the measurement error on the initial position of the receiver. Considering that the errors on each phase measurement are Gaussian centered at zero, and that these errors are distributed identically for each transmitter and independent of each other, the extended horizontal dilution of the accuracy can be calculated from the formula: VOC (E _x ) = (H ^t H) ^_1 at _ERE , with VOC (E _x ) the covariance matrix of the error on the estimated position of the receiver, and σ¾ _ΕΚΕ the variance of the error on the measure , or "User Equivalent Range Error" in English. By noting σ _¾ the elements of cov (sx) and Dij the elements of (H'H) ^"1 , we obtain: EHDOP = JO ₁ + D ₂₂ = ^{(Tll + (T22} .

^CT UERE

 An extended horizontal dilution value of the accuracy between 10 and 40 is considered acceptable, the results obtained for the positions PO to P4 are therefore correct. Nevertheless, the extended horizontal dilution value of the accuracy obtained for the P4c position defined above is excellent. This shows that it is interesting and necessary to use the method according to the invention during the evolution of the receiver within the system to reduce the errors accumulating along the trajectory.

As explained previously, the number of transmitters n _p i of the system 1 is a function of the dimension m of the positioning and the number of measurements k _pt made for different positions of the receiver 2: # 2 · (1 + ^~ ) ≤ n _pl F _or example, for m = 3 corresponding to a 3D positioning, the minimum number of transmitters n _p i is equal to 5 so three different positions are used to make three measurements k _pt: 3 (1 + 1/3) = 4. If only one measure k _pt is used, to have the position of the receiver quickly, you need: 3 (1 + 1) = 6 transmitters.

 The invention is not limited to the examples which have just been described.

 Other signals than the GPS and GNSS signals can be used, for example WIFI, 4G, GSM or radio signals.

The methods according to the invention can be coupled with other geolocation methods, such as methods using a mobile reader, beacons and a geolocation and guidance application executable on said reader. The invention can be implemented in locations where collective sports are practiced, especially indoors, for example by fixing or incorporating a system in football cages or handball to calculate in real time the position of the players, or on construction sites, for example for installing false ceilings, using one or more strips made up of a network of about ten antennas, or in large shopping centers.

 The invention can be used outdoors, to overcome the base station.

 The expression "comprising one" must be understood as synonymous with the expression "comprising at least one", except when the opposite is specified.

Claims

A method of locating at least one receiver (2) within a positioning system (1), the system comprising:  at least two generators (PL1, PL2), each generator transmitting on the same carrier at least two signals each having a different code, and  a receiver (2) configured to detect the signals emitted by the generators (PL1, PL2), process in which the receiver (2) measures, for each of the generators (PLI, PL2), the phase difference (δφ ⁷ ) between the two signals emitted by the generator (PLj), and according to these phase difference measurements (δφ ⁷ ), at least one geometric magnitude representative of the position (x _r , y _r ) of the receiver (2) relative to the generators (PLI, PL2) is calculated, in order to locate the receiver (2) within the positioning system (1). 2. Method according to claim 1, wherein the two signals emitted by each generator (PLj) are emitted from two transmission zones (PLj, PLj ₂ ) of the generator distant from each other by a distance predefined (di ₂ ). 3. Method according to the preceding claim, wherein the geometric magnitude representative of the position (x _r , y _r ) of the receiver (2) relative to a generator (PLj) is the arrival angle (cy) of the signals emitted by the generator (PLj) on the receiver (2), according to the predefined distance

between the two emission zones (PLji, PLj ₂ ) of the enerator (PLj) and phase difference measurements (δφ ⁷ ), and defined by:

4. Method according to claim 1 or 2, wherein the geometric magnitude representative of the position (x _r , y _r ) of the receiver (2) with respect to a generator (PLj) is the distance separating them, a function of the distances (di , d ₂₎ between the position (x _ai, y _ai, x _{a2, a2} y) of each transmit zone (PLji, PLj ₂₎ of the generator (PLj) and the position (x _r, y _r) receiver (2), defined by: d ₂ - d _x = J (x a ₂ -x _r f + (y ₂ - y _r f - J (x _al- x _r f + (y _al- y _r f = δφ. 5. Method according to any one of the preceding claims, wherein the two signals emitted by each generator (PLj) are derived from at least two antennas (PLji, PLj ₂ ) belonging to the generator and distant from each other a predefined distance 6. Method according to the preceding claim, wherein the predefined distance (di ₂ ) according to which the two antennas (PLji, PLj ₂ ) of the same generator (PLj) are distant from each other is equal to the length waveform (λ) of the carrier of the signals transmitted by the antennas (PLji, PLj ₂ ).  7. Method according to any one of the preceding claims, wherein the signals emitted by the same generator (PLj) are synchronized with each other.  8. Method according to any one of the preceding claims, wherein each generator (PLj) transmits on a different frequency.  9. Method according to any one of the preceding claims, wherein the frequency of the signals emitted by the generators (PLI, PL2) is equal to 1.575 GHz, the signals being in particular GNSS Galileo type.  10. Method according to any one of the preceding claims, being implemented indoors (indoor).  11. Positioning system (1), comprising:  at least two generators (PL1, PL2), each generator transmitting on the same carrier at least two signals each having a different code, and  a receiver (2) detecting the signals emitted by the generators (PLI, PL2), the system (1) being configured so that: the receiver (2) measures, for each of the generators (PLI, PL2), the phase difference (δφ ⁷ ) between the two signals emitted by the generator (PLj), and according to these phase difference measurements (δφ ⁷ ), at least one geometric magnitude representative of the position (x _r , y _r ) of the receiver (2) relative to the generators (PL1, PL2) is calculated, in order to locate the receiver (2) within the positioning system (1). Receiver (2) intended to be used within a positioning system (1) comprising at least two generators (PLI, PL2), each generator transmitting on the same carrier at least two signals each having a different code, the receiver (2) detecting the signals emitted by the generators (PLI, PL2), the receiver (2) being configured to: measuring, for each of the generators (PLI, PL2), the phase difference (δφ ⁷ ) between the two signals emitted by the generator (PLj), and as a function of these phase difference measurements (δφ ⁷ ), that at least one geometric magnitude representative of the position (x _r , y _r ) of the receiver (2) with respect to the generators (PL1, PL2) be calculated, in order to locate the receiver (2) within the positioning system (1).  13. Receiver according to the preceding claim, comprising a phase locked loop configured to measure the phase (φ) of the signals emitted by the generators (PLI, PL2).  14. Generator (PLI) for use in a positioning system (1), said system comprising at least one other generator (PL2) and a receiver (2) configured to detect the signals emitted by said generator and the another generator (PLI, PL2), said generator (PLI) being configured to transmit on the same carrier at least two signals each having a different code, the receiver (2) being configured to measure the phase difference (δφ) between said two signals emitted by the generator (PLI).